1. Field of the Invention
The present invention relates to high-frequency connectors used for high-frequency devices, such as high-powered, high-frequency devices.
2. Description of the Related Art
There are several conventional types of connectors used for high-frequency devices, including, for example, conductors commonly known as SMT, N, and BNC connectors. Effective use of these connectors depends on their capabilities and intended uses. Each type of connector includes a housing which serves as an external conductor, and a central conductor. Beryllium copper having high tensile strength is used as a base material for the housing and the central conductor. Further, generally, nickel plating is applied, and gold plating or silver plating is further applied on the underlying nickel-plated layer, if necessary.
When high-frequency electric currents pass through a conductor, a skin effect occurs. The skin depth decreases as the permeability of a magnetic metal increases. The skin depth (.delta.) is expressed by the following formula: EQU .delta.=1/.cuberoot.(.pi.f.sigma..mu..sub.o .mu..sub.r)
where
f: frequency of high-frequency currents; PA1 .sigma.: electric conductivity of conductor; PA1 .mu..sub.o : vacuum permeability; and PA1 .mu..sub.r : relative permeability.
As the permeability increases, the skin depth decreases and the electric current density of the surface layer increases.
Even if the base material is nonmagnetic, when strong high-frequency currents pass through a conductive channel having a magnetic conductive coating film, the electric current density of the surface layer increases abnormally and intermodulation distortion occurs.
As described above, in a conventional high-frequency connector, a nickel-plated layer is formed by electroplating to form a surface plated layer on the base material or to form a plated layer on top of which gold or silver plating is added. The nickel-electroplated layer has high permeability at high frequencies, for example, a relative permeability .mu..sub.r of approximately 3.0 at 1 GHz. Therefore, when high-level, high-frequency currents pass through the nickel-plated layer, intermodulation distortion may occur in some cases. In particular, with the miniaturization of devices, the connectors used have also been miniaturized. If the electric current density further increases, intermodulation distortion will occur more easily.